The effects of stress on equilibrium point defect populations and on dopant diffusion in strained semiconductors are reviewed. The thermodynamic relationships presented permit the direct comparison of hydrostatic and biaxial stress experiments and of atomistic calculations of defect volumetrics for any proposed mechanism. Experiments on the effects of pressure and stress on the diffusivity of B and Sb are reviewed. The opposite effects of hydrostatic compression and of biaxial compression on the diffusivity are a consequence of the non-local nature of the point defect formation volume. Comparisons between these effects are made to determine quantitatively the anisotropy of the migration volume. The requirements to permit the prediction of the effect of an arbitrary stress state on diffusion in an arbitrary direction are discussed.